1. Field of the Invention
The present invention relates to a tone control apparatus and, more particularly, to a tone control apparatus in a sound system having audio signal outputs of front and rear channels.
2. Description of Background Information
As a tone control apparatus, it is a general way to control treble (high frequency sound) and bass (low frequency sound) levels in accordance with key operations. In the case of tone control apparatuses provided in a sound system having audio outputs of a plurality of channels, the tone control is performed in such a manner that the same frequency response characteristic is used for all of the channels.
In what is called a 4-speaker accommodating onboard (for mounting in a vehicle) sound system in which each of the front and rear channels has audio outputs of the right and left channels, generally, speakers of a small diameter are arranged on the front side and speakers of a relatively larger diameter are arranged on the rear side because of restrictions on the mounting of speakers in the vehicle cabin In the tone control apparatus provided in such an onboard type sound system, the user may operate a bass tone control knob to raise the bass level of the sound outputs for instance in order to compensate the insufficiency of the bass sound. In such a case, although the bass level in the whole acoustic outputs can be increased, a problem arises that the front speakers produce distortions of large degrees while the permissive driving power of the speakers are exceeded because of the small diameter of the front speakers mentioned before. On the other hand, if the user raises the treble level of the sound outputs by operating a treble control knob because of the insufficiency of the treble sound at the front seat, a problem arises such that, the sound level of the treble range becomes excessively high for passengers sitting on the rear seat because of the nearness of the rear speakers and the rear seats, giving an unpleasant feeling.